Pulmonary Infections PDF

# PULMONARY INFECTIONS ## I. PNEUMONIA - Infection of the lung parenchyma. - Occurs when normal defenses are impaired (e.g., impaired cough reflex, damage to mucociliary escalator, or mucus plugging) or organism is highly virulent. - Clinical features include fever and chills, productive cough wit...

# PULMONARY INFECTIONS ## I. PNEUMONIA - Infection of the lung parenchyma. - Occurs when normal defenses are impaired (e.g., impaired cough reflex, damage to mucociliary escalator, or mucus plugging) or organism is highly virulent. - Clinical features include fever and chills, productive cough with yellow-green (pus) or rusty (bloody) sputum, tachypnea with pleuritic chest pain, decreased breath sounds, crackles, dullness to percussion, and elevated WBC count. - Diagnosis is made by chest x-ray, sputum gram stain and culture, and blood cultures. - Three patterns are classically seen on chest x-ray: - Lobar pneumonia - consolidation all over a lobe - bacterial - Bronchopneumonia - patchy consolidation - viral - Interstitial pneumonia - no consolidation but inflammation of interstitium ## II. LOBAR PNEUMONIA - Characterized by consolidation of an entire lobe of the lung. - Usually bacterial; most common causes are Streptococcus pneumoniae (95%) and Klebsiella pneumoniae. - Classic gross phases of lobar pneumonia: - Congestion - due to congested vessels and edema - Red hepatization - due to exudate, neutrophils, and hemorrhage filling the alveolar air spaces, giving the normally spongy lung a solid consistency. - Gray hepatization - due to degradation of red cells within the exudate - Resolution ## III. BRONCHOPNEUMONIA - Characterized by scattered patchy consolidation centered around bronchioles; often multifocal and bilateral. - Caused by a variety of bacterial organisms. ## IV. INTERSTITIAL (ATYPICAL) PNEUMONIA - Characterized by diffuse interstitial infiltrates. - Presents with relatively mild upper respiratory symptoms (minimal sputum and low fever); 'atypical' presentation - Caused by bacteria or viruses. ## V. ASPIRATION PNEUMONIA - Seen in patients at risk for aspiration (e.g., alcoholics and comatose patients) - Most often due to anaerobic bacteria in the oropharynx. ## VI. TUBERCULOSIS (TB) - Due to inhalation of aerosolized Mycobacterium tuberculosis. - Primary TB arises with initial exposure. - Results in focal, caseating necrosis in the lower lobe of the lung and hilar lymph nodes that undergoes fibrosis and calcification, forming a Ghon complex. - Primary TB is generally asymptomatic, but leads to a positive PPD. - Secondary TB arises with reactivation of Mycobacterium tuberculosis. - Reactivation is commonly due to AIDS; may also be seen with aging. - Occurs at apex of lung (relatively poor lymphatic drainage and high oxygen tension). - Forms cavitary foci of caseous necrosis; may also lead to miliary pulmonary TB or tuberculous bronchopneumonia. - Clinical features include fevers and night sweats, cough with hemoptysis, and weight loss. - Biopsy reveals caseating granulomas; AFB stain reveals acid-fast bacilli. - Systemic spread often occurs and can involve any tissue; common sites include meninges (meningitis), cervical lymph nodes, kidneys (sterile pyuria), and lumbar vertebrae (Pott disease). ## VII. TABLE 9.1: CAUSES OF LOBAR PNEUMONIA | ORGANISM | HIGH-YIELD ASSOCIATIONS | |---|---| | Streptococcus pneumoniae | Most common cause of community-acquired pneumonia and secondary pneumonia (bacterial pneumonia superimposed on a viral upper respiratory tract infection); usually seen in middle-aged adults and elderly | | Klebsiella pneumoniae | Enteric flora that is aspirated; affects malnourished and debilitated individuals, especially elderly in nursing homes, alcoholics, and diabetics. Thick mucoid capsule results in gelatinous sputum (currant jelly); often complicated by abscess | ## VIII. TABLE 9.2: CAUSES OF BRONCHOPNEUMONIA | ORGANISM | HIGH-YIELD ASSOCIATIONS | |---|---| | Staphylococcus aureus | 2nd most common cause of secondary pneumonia; often complicated by abscess or empyema | | Haemophilus influenzae | Common cause of secondary pneumonia and pneumonia superimposed on COPD (leads to exacerbation of COPD) | | Pseudomonas aeruginosa | Pneumonia in cystic fibrosis patients | | Moraxella catarrhalis | Community-acquired pneumonia and pneumonia superimposed on COPD (leads to exacerbation of COPD) | | Legionella pneumophila | Community-acquired pneumonia, pneumonia superimposed on COPD, or pneumonia in immunocompromised states; transmitted from water source. Intracellular organism that is best visualized by silver stain | ## IX. TABLE 9.3: CAUSES OF INTERSTITIAL (ATYPICAL) PNEUMONIA | ORGANISM | HIGH-YIELD ASSOCIATIONS | |---|---| | Mycoplasma pneumoniae | Most common cause of atypical pneumonia, usually affects young adults (classically, military recruits or college students living in a dormitory). Complications include autoimmune hemolytic anemia (IgM against I antigen on RBCs causes cold hemolytic anemia) and erythema multiforme. Not visible on gram stain due to lack of cell wall | | Chlamydia pneumoniae | Second most common cause of atypical pneumonia in young adults | | Respiratory syncytial virus (RSV) | Most common cause of atypical pneumonia in infants | | Cytomegalovirus (CMV) | Atypical pneumonia with posttransplant immunosuppression or chemotherapy | | Influenza virus | Atypical pneumonia in the elderly, immunocompromised, and those with preexisting lung disease. Also increases the risk for superimposed S aureus or H influenzae bacterial pneumonia | | Coxiella burnetii | Atypical pneumonia with high fever (Q fever); seen in farmers and veterinarians. Coxiella is a rickettsial organism, but it is distinct from most rickettsiae because it: causes pneumonia, does not require arthropod vector for transmission, survives as highly heat-resistant endospores, and does not produce a skin rash. |